When cooling the engine and the radiator of a construction machine, such as a hydraulic excavator, a wheel loader or the like, cooling air is usually supplied by way of driving, together with the engine, a fan which is directly connected to the engine. This system, however, requires an aperture sufficiently large for introducing and discharging the cooling air, and, therefore, there are limitations in how well the sound of the engine can be insulated. In order to solve the above problem, a configuration shown in FIG. 4 adapted to be disposed on the revolving super structure of a hydraulic excavator, wherein an engine 11 is disposed separately from a cooling unit 12 comprised of a radiator and an oil cooler, and an engine room 13 is enclosed in a sound insulating enclosure 14. According to this configuration, cooling air is supplied to the radiator and the oil cooler by driving an exclusive cooling fan 15 of the cooling unit 12.
FIG. 5 shows an example of conventional configurations for driving a cooling fan 15 disposed in an air passage 16 by means of a hydraulic motor 17, wherein the hydraulic motor 17 is driven only in the forward direction by means of hydraulic oil supplied from a hydraulic pump 18, which is rotated by an engine 11.
A radiator 12a, which is one of the two principal components of a cooling unit 12, is connected to a water jacket (not shown) of the engine 11 via a cooling water output pipe 21 and also connected to a water pump (not shown) of the engine 11 via a cooling water return pipe 22. An oil cooler 12b, which is the other principal component of the cooling unit 12, is adapted to the cool hydraulic oil that becomes hot as it circulates in a hydraulic circuit. The hydraulic circuit is comprised of a hydraulic pump 23 rotated by the engine 11, hydraulic equipment such as a control valve 24 for controlling the direction and the flow rate of the hydraulic oil discharged from the hydraulic pump 23, and a hydraulic actuator 25 which may be a hydraulic cylinder and is adapted to be operated by means of the hydraulic oil controlled by the control valve 24. The oil cooler 12b is disposed in a tank line 27 that extends from an oil discharge port of the control valve 24 to a tank 26.
In either one of the direct-connection system and the separate installation system described above, the cooling fan is rotated only in one direction so that the cooling air, too, flows in one direction, either for discharge or intake.
Particularly in cases where a cooling fan is directly connected to an engine, a revolution speed of the fan is normally in proportion to the engine speed, and cooling air is supplied to the cooling unit even immediately after starting the engine, when the temperatures of the engine cooling water, the hydraulic oil and the like have not yet reached the warm-up temperature appropriate for operation of the machine. Feeding cooling air in such a situation further increases the length of time of warm-up operation.
As the cooling air is fed only in one direction, dead leaves, debris or the like tend to enter the radiator and the oil cooler and often plug them.
In an effort to solve the above problems, the inventor of the present invention has focused on the fact that the radiator and the oil cooler respectively obtain cooling air for their own by driving their own dedicated cooling fans. Accordingly, an object of the present invention is to reduce the duration of a warm-up operation of the hydraulic equipment by means of reversing the rotation direction of the cooling fans and discharge debris stuck in the radiator or the oil cooler by using air blowing in the reverse direction.